The present invention relates to a suspension system for a vehicle, and more specifically to a shape memory alloy suspension component to regulate the suspension characteristics of a vehicle.
A suspension system in a vehicle is usually provided with various suspension components, such as springs, dampers, anti-sway bars, stabilizer bars and the like which regulate the handling characteristics of the vehicle. Such suspension components are typically arranged between the vehicle wheel and vehicle body. Inherent characteristics of the components necessarily limit the suspension system to fixed properties and thus fixed handling characteristics. That is, each system has its own characteristics, which cannot be varied. This is a disadvantage when certain handling characteristics may be preferred for one road condition and not preferred for another road condition.
A particular example of this problem is provided by current sport utility vehicles which may be driven on both highway and off-road environments. The sport utility vehicle must incorporate a suspension that is applicable for each environment. Because the suspension system provides fixed characteristics, which require trade-offs that allow usage in both environments the suspension system is prevented from being optimized for either usage.
The term Shape Memory Alloys (SMA) is applied to that group of materials that demonstrate the ability to change shape, stiffness, position, natural frequency, and other mechanical characteristics in response to temperature or electromagnetic fields. Materials, both organic and metallic, possessing shape-memory, are known. An article made from such materials can be deformed from an original, heat-stable configuration to a second, heat-unstable configuration. The article is said to have shape-memory for the reason that upon application of heat alone it can be caused to revert, or attempt to revert, from its heat unstable configuration to its original heat-stable configuration, i.e., it xe2x80x9cremembersxe2x80x9d its original shape.
The ability to display shape-memory is a result of the fact that the alloy undergoes a reversible transformation from an austenitic state to a martensitic state with a change in temperature. An article made from such an alloy is easily deformed from its original configuration to a new configuration when cooled to a temperature below which the alloy is transferred from the austenitic state to the martensitic state.
Although a relatively wide variety of alloys are know to exhibit the shape memory effect, preferred are those that can recover substantial amounts of strain or that generate significant force upon changing shape. The best known and most readily available SMA is Nitinol, an alloy of nickel and titanium. Other such SMAs are nickel-titanium alloys and copper-base alloys such as CuZnAl and CuAlNi.
Actuators have heretofore been developed which employ shape-memory alloys or materials. However, such materials and alloys have not been incorporated into suspension systems.
It is therefore desirable to provide shape memory alloy suspension component to allow the suspension characteristics of a vehicle to be regulated.
The Shape Memory Alloy (SMA) suspension system according to the present invention generally includes a SMA suspension component, an actuator and a controller. It is known that SMAs respond to a shift in temperature above and below a phase transformation temperature to actuate or change a mechanical property of the SMA. The particular mechanical characteristic of the SMA suspension component, such as shape, stiffness, position, natural frequency, can therefore be altered. Altering the mechanical characteristic of the SMA suspension component thereby alters the kinematic properties of the vehicle wheel relative to the vehicle body and the suspension characteristics of the vehicle.
To alter the SMA suspension component, the present invention attaches an actuator to the vehicle body in the vicinity of the SMA component. The actuator referably generates heat, an electromagnetic field or electric current to shift the SMA component temperature above or below a phase transformation temperature to actuate or change a mechanical characteristic of the SMA suspension component in a known manner. Preferably, a controller is in communication with the actuator. The controller controls the actuators automatically based upon sensors which communicate with the SMA suspension components or alternatively or additionally by manual input from the driver.
In one disclosed embodiment a SMA suspension component spring is illustrated. The spring is manufactured of SMA such that the adjustable mechanical characteristic is the spring height. Changing the spring height thereby alters the vehicle handling characteristics.
In another disclosed embodiment a SMA suspension component stabilizer bar is illustrated. The stabilizer bar is manufactured of SMA such that the adjustable mechanical characteristic is the shape of the stabilizer bar. In the disclosed embodiment, the SMA stabilizer bar is maintained in a first shape which clears the vehicle frame. The function of the stabilizer bar is substantially removed and the vehicle handling characteristics are optimized for a first condition such as an off-road environment. The off-road performance is thereby improved as the suspension articulation and traction are increased by reducing the function of the stabilizer bar.
When the SMA characteristics of the stabilizer bar are inactivated the stabilizer bar shape is expanded to contact a fixed vehicle component such as a vehicle frame component. By bringing the stabilizer bar into contact with the frame, the flexibility of the stabilizer bar is reduced and the vehicle handling characteristics are optimized for a second condition such as an on-road environment.
The SMA suspension components according to the present invention thereby allows the suspension characteristics of a vehicle to be changed to suit desired handling and environment conditions.